High floor pivoted mast drilling rig

ABSTRACT

A framework type mast structure is pivotally mounted on a base structure. A self-supporting pedestal structure including a gin pole structure which is pivotally mounted on the base structure adjacent the mast structure. The pedestal structure with the gin pole is tilted to vertical position, and the gin pole secured. Sheaves carried by the gin pole cooperate with a sling line which runs to and is looped over the hook of the traveling block of the drilling rig for purposes of raising the mast structure to an upright position. A second self-supporting pedestal structure is tilted into position on the base structure on the other side of the mast structure and below a racking board assembly carried by the mast structure which is used to support the lower end of racked drill pipe independently of the mast structure. A rotary table is supported independently of the mast structure by means of a horizontal support structure which extends through the framework of the mast structure and is supported by the two pedestal structures. A working floor is carried by the gin pole pedestal structure which, together with the rotary table and the pipe supporting floor of the second pedestal structure, is positioned at an elevated location above the base structure. In a second embodiment, a separate gin pole structure is not used and the mast raising sheaves are instead mounted on the main body of the first pedestal structure.

United States Patent 1 1 Branham July 24, 1973 HIGH FLOOR PIVOTED MAST DRILLING RIG [75] Inventor: Donald R. Branham, Houston, Tex.

[73] Assignee: Pyramid Derick and Equipment Corporation, Houston, Tex.

221 Filed: Apr. 6, 1971 211 Appl. No.: 131,630

[52] U.S. Cl 173/151, 52/110, 52/116, 175/52 [51] Int. Cl. E2111 15/00 [58] Field of Search ..52/120,111,121,

Primary Examiner-Ernest R. Purser Attorney-Jack W. Hayden 57 ABSTRACT A framework type mast structure is pivotally mounted 4a on a base structure. A self-supporting pedestal structure including a gin pole structure which is pivotally mounted on the base structure adjacent the mast structure. The pedestal structure with the gin pole is tilted to vertical position, and the gin pole secured. Sheaves carried by the gin pole cooperate with a sling line which runs to and is looped over the hook of the traveling block of the drilling rig for purposes of raising the mast structure to an upright position. A second selfsupporting pedestal structure is tilted into position on the base structure on the other side of the mast structure and below a racking board assembly carried by the mast structure which is used to support the lower end of racked drill pipe independently of the mast structure. A rotary table is supported independently of the mast structure by means of a horizontal support structure which extends through the framework of the mast structure and is supported by the two pedestal structures. A working floor is carried by the gin pole pedestal structure which, together with the rotary table and the pipe supporting floor of the second pedestal structure, is positioned at an elevated location above the base structure. In a second embodiment, a separate gin pole structure is not used and the mast raising sheaves are instead mounted on the main body of the first pedestal structure. 9

11 Claims, 7 Drawing Figures PAIENTEO M24815 3'. 147. 695

SHEET 2 BF 3 Jana/a fl. Brow/3am INI'ENTOR M W. Magda ATTORNEY I HIGH FLOOR PIVOTED MAST DRILLING RIG BACKGROUND OF THE INVENTION This invention relates to a high floor pivoted mast drilling rig for drilling bore holes into the earth. While not limited thereto, the invention is particularly useful in drilling oil wells, gas wells, and other mineral pro ducing bore holes into the earth.

As oil wells are drilled deeper and deeper, it becomes more desirable to use drilling rigs having taller masts and higher substructures. The taller the mast, the fewer the pipe joints that have to be broken in a given length of drill pipe coming out of the hole, thus enabling trips to be made in a more rapid manner. Also, deeper wells encounter high pressures, thus necessitating the use of more and larger safety equipment between the well head and the working floor of the drilling rig. To provide clearance for such safety equipment, the substructure supporting the working floor must be relatively high. The taller the mast and substructure, the greater the problems involved in erecting, disassembling and transporting the rig from one location to another.

The labor and time expended in assembling and disassembling the drilling rig can be minimized by utilizing a pivoted mast type of drilling rig wherein the mast is pivotally connected to a base structure and is raised to its upright position by means of a gin pole structure secured to the base structure adjacent the mast pivot point. The elevated working floor is provided by a floor structure carried by the mast and additional floor structures which are pinned to the mast and to the gin pole structure. Atypical form of drilling rig of this type is described in U. S. Pat. No. 3,262,237 granted to Jenkins et al. on July 26, 1966.

While drilling rigs of the type described in this U.S. Pat. No. 3,262,237 do largely achieve the desired objective of simplifying the assembly and disassembly procedures, they nevertheless suffer from various disadvantages and drawbacks. For one thing, the setback portion of the working floor which carries the weight of the racked drill pipe is pinned to and supported in part by the drilling mast. This places an undesirable additional strain on the mast structure. For another thing, the rotary table is supported by a portion of the floor structure which is mounted on the drilling mast. Consequently, vibrations and other movements of the rotary table occurring when drilling through hard formations are transferred directly to the drilling mast which, in turn, tends to cause the whole mast to shake or vibrate. These problems can, of course, be overcome in part by strengthening the mast by using a more elaborate framework construction for the mast structure and by using heavier structural members for such framework. This, however, increases the expense of the mast structure and the expense and difficulty of transporting same from one well site to another.

SUMMARY OF THE INVENTION It is anobject of the invention, therefore, to provide wherein rotary table vibrations are not directly transferred to the mast structure.

In accordance with one feature of the invention, a high-floor pivoted-mast drilling :rig comprises a base structure and a framework type mast structure pivotally mounted on the base structure. A first selfsupporting pedestal structure is mounted on the base structure on one side of the mast structure pivot axis for supporting a working floor at an elevated position above the base structure. A racking board assembly is carried by the mast structure at an upper location thereon and extends outwardly from the mast structure on the side farthest removed from the first pedestal structure when the mast structure: is in an upright position. A second self-supporting pedestal structure is mounted on the base structure on the other side of the mast structure pivot axis and below the racking board assembly for supporting the lower end of racked drill pipe independently of the mast structure and at an elevated position above the base structure.

In accordance with another feature of the invention, the drilling rig includes a rotary table support structure which extends through the framework of the mast structure and is independently supported by first and second self-supporting pedestal structures located on opposite sides of the mast structure. Such support structure serves to support a rotary table at an elevated position above the base structure independently of the mast structure. 1

For a better understanding of the present invention, together with other and further objects and features thereof, reference is had to thefollowing description taken in connection with the accompanyingdrawings,

the scope of the invention being pointedout in the appended claims.

BRIEF DESCRIPTIONOF THE DRAWINGS Referring to the drawings:

FIG. 1 is an elevational view of a high-floor pivotedmast drilling rig constructed in accordance with the present invention;

FIG. 2 is an elevational view of the mast portion of the FIG. 1 drilling rig taken at right angles to the elevational view of FIG. 1 along section line 2-2 thereof;

FIG. 3 is a plan view taken along section line 33 of FIG. 1;

FIGS. 4, 5 and 6 show different steps in the assembly and erection of the FIG; 1 drilling rig; and

FIG. 7 is a partial elevational view showing modified forms of construction for portions of the FIG. 1 drilling rig.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-3, there is shown a high-floor pivoted-mast drilling rig in its assembled condition as it would appear when drilling an oil well or gas well or other type of borehole into the earth. The drilling rig includes a relatively tall substructure 10 for supporting two side frames of the mast 13 are pivotally mounted in a pair of shoes 17, one of which is mounted on each of the box structures 15 and 16 of the base structure 14.

The substructure 10 further includes a first selfsupporting pedestal structure 18 mounted on the base structure 14 on one side of the mast structure pivot shoes 17. The pedestal structure 18 is of a box-like framework type construction having four legs 19 which are detachably pinned to four shoes 20 mounted on the base structure 14. Two of the shoes 20 are mounted on the base box structure 15, while the other two are mounted on the base box structure 16. Legs 22, 23 form gin pole structure 21, the legs 22 being carried by the pedestal structure 18, and legs 23 are connected to legs 22 at their upper end and extend therefrom and are pinned on the base structure 14. A pair of legs 22 is provided, one each on each side of the pedestal structure 18, and a pair of legs 23, one being pinned at its lower end to structure 15 and one being pinned at its lower end to structure 16. A plurality of sheaves 24, 25, and 26 is rotatably mounted at the top of the gin pole 21 by means of a shaft 27 which, as indicated in FIG. 2, extends between the spaced gin pole legs 22 and 23 where they are connected at their upper ends. The center sheave is mounted so that it can also slide back and forth on the shaft 27. A walkway support extension 28 is pivotally pinned across the back side of the pedestal structure 18 and, when horizontally extended, is supported by a brace 29 extending therefrom to the pedestal structure 18.

The substructure 10 also includes a second selfsupporting pedestal structure 30 mounted on the base structure 14 on the other side of the mast structure pivot shoes 17. This second pedestal structure 30 is also of a box-like framework construction having four legs 31 detachably pinned to 4 shoes 32 mounted on the base structure 14, 2 such shoes being mounted on the base box structure 15 and the other two being mounted on the base box structure 16 thereof. A working floor surface 33 covers the top of the pedestal structure 30. As indicated in FIG. 3, the center portion of this surface 33 is formed by a series of wooden planks 34 which form a pad for supporting the lower ends of lengths of racked drill pipe. A walkway extension 35 is pivotally pinned across the right-hand side of the pedestal structure 30, such extension 35 being supported by a brace 36 when in its extended position.

The mast structure 13 is of a framework construction and includes an upper tower portion 13a and a lower stub portion 13b, the latter of which narrows down to provide the feet which are pivotally pinned to the base structure shoes 17. The tower portion 13a is made up in sections which are pinned together and the lowermost section thereof is, in turn, pinned'to the stub section 13b. The tower portion 13a is comprised of four vertically extending frame members 37 defining the four corners thereof and interconnected on, three sides of the mast 13 by series of horizontal and diagonal braces 38. No cross braces are provided on the side of the mast 13 facing the second pedestal structure 30 so that this side of the mast is open. As indicated in FIGS. 2 and 3, the stub portion 13b is comprised of a pair of side frames 40 and 41 which extend downwardly and are pinned to the base structure pivot shoes 17.

When in its upright position as shown, the mast structure 13 is pinned to the top of the gin pole structure 21 by means of coupling brackets indicated at 42. A pair of spaced apart sheaves 43 (only one of which is visible in FIG. 1) are rotably carried near the top of the stub portion 13b for cooperating with the gin pole sheaves 24 and 26 when raising the mast 13 to its upright position. A pair of brackets 44 are mounted on the rearward legs 37 of the mast 13, also for use in raising the mast 13.

The mast structure 13 carries a hoisting mechanism which includes a traveling block 45 which is suspended from a crown block 46 by multiple loops of a drilling line 47. The live end of the drilling line 47 leaves the crown block 46 by way of a sheave 48 and runs downwardly to the wench drum of a drawworks 49. The mast structure 13 further carries a racking board assembly 50 at an upper location thereon. The racking board assembly 50 extends outwardly over the second pedestal structure 30 and includes the usual pipe racks for holding the upper ends of lengths of drill pipe. Several stands of drill pipe are indicated at 51. The lower ends of such pipe stands 51 rest on the pad 34 on top of the pedestal structure 30 and the upper ends are held by the racks in the assembly 50.

The drawworks 49 is positioned adjacent the first pedestal structure 18 and is supported by a suitable support structure 52. Drawworks 49 is driven by a set of engines 53 which are supported by an appropriate support structure 54, the drive linkage between the engines 53 and drawworks 49 being omitted for sake of simplicity.

The drilling rig further includes a rotary table support structure which extends through the framework of the mast structure 13 and is supported by the first and second pedestal structures 18 and 30 at an elevated position above the base structure 14 for supporting a rotary table 55 independently of the mast structure 13. In the present embodiment, this support structure takes the form of a skid structure 56 which extends over and rests on the cross beams of an upper portion of the first pedestal structure 18. The right-hand end of the skid 56 extends through the framework of the mast structure 13 and is pinned to the second or right-hand pedestal structure 30. In addition to the rotary table 55, the skid 56 carries an independent rotary drive and catworks mechanism 57. The rotary drive portion of this mechanism 57 is operatively coupled to the rotary table 55 by an appropriate linkage mechanism which, for simplicity of illustration, is not shown in the drawings. As indicated in FIG. 1, the center of the rotary table 55 is located within the confines of the framework of the mast structure 13. Since there is no direct connection or contact between the skid 56 and the mast structure 13, the rotary table 55 is thus supported independently of the mast structure 13. This minimizes the transfer of vibrations from the rotary table 55 to the mast structure 13. The upper end of a string of drill pipe 58 is shown in FIG. 1 as being held by the rotary table 55.

For simplicity of illustration, the blowout preventors.

and other safety equipment located below the rotary table 55 are not shown. The deck panelsforming the working floor 11 are laid out around the skid 56 and supported at a slight elevation above such skid 56 by means of support braces and cross beams carried by the first pedestal structure 18 and the walkway support extension 28.

The drilling rig of FIGS. l-3 is a portable type drilling rig which may be transported to a well site in a disassembled condition and then assembled and erected to the condition shown in FIGS. 1-3. Referring now to FIGS. 4-6, the method of assembling the drilling rig will now be considered. As indicated in FIG. 4, the first step is to locate the base structure 14, the drawworks support 52 and the engine support 54 in the proper relationship to one another on the ground surface 12. At this time, the tie beams running between the two side boxes and 16 of the base structure 14 are installed. Next, the gin pole supporting pedestal 18 is erected in horizontal position and then elevated to vertical position with the aid of a separate truck mounted gin pole. FIG. 4 illustrates in dotted line the gin pole pedestal 18 in the horizontal position, and in this position, the lefthand legs of the pedestal structure 18 are pinned to the left-hand pair of shoes 20 on the base structure 14. The pedestal 18 is then pivoted to the upright position shown in solid line by means of the separate gin pole truck, and the righbhand legs of the pedestal 18 are then pinned to the right-hand shoes 20 on the base structure 14. Alternatively, the pedestal structure 18 could be raised to the upright'pos'ition by means of a hydraulic cylindrical mechanism connected between the base structure 14 and the left-hand side of the pede'stal structure 18. Following erection of the pedestal structure 18, the drawworks 49 and the drawwork engines 53 are set in place on their respective support structures 52 and 74, this condition being indicated in FIG. 5. The gin pole 21 is then formed by connecting legs 22 at their lower end to the top of structure 18, connecting the lower end of legs 23 to, substructure l4 and the upper ends of legs 22, 23 together with shaft 27 extending between the legs 22, 23 on one side with the legs 22, 23 on the other side of structures 18 and 14.

Proceeding now to the erection of the mast structure 13, the stub section 13b thereof is placed in a horizontal position as indicated in outline form in FIG. 5, and the feet of the two stub section side frames are pinned in place in the pivot shoes 17. With the aid of the separate gin pole truck and a suitable support stand, the lowermost section of the tower structure 13a is pinned to the stub section 13b and thereafter the further sections of the tower structure 13a are pinned to one another in an end-to-end manner to form the completed tower structure, the support stand being moved further to the right as each section is added. The crown block structure is pinned to the far end of the last such tower section. The traveling block 45 is then positioned within the mast structure 13 and the drilling line 47 is reeled off the drawworks 49 and reaved between the crown block 46 and the traveling block 45, the dead end of line 47 being connected to an appropriate anchor on the base structure 14. At this time, the drilling line 47 passes over the gin pole sheave located behind the gin pole sheave 24 in FIG. v5.

Thenext step is to string up a sling line 60. One end ofthis sling line 60 is tiedto the forwardmost one of the brackets 44 in FIGS. From there, the sling line 60 runs over the gin pole sheave 24, then over the forwardmost one of the mast-maimed sheaves 43 and is then looped over the hook of the traveling block 45. From there, the sling line 60 passes back over the rearwardmost one of the mast-mounted sheaves 43, then back over the rearward gin pole sheave 26 and is then tied to the rearward one of the brackets 44. To raise the mast 13, the drawworks 49 is operated to move the traveling block 45 to the right. This pulls the lower spans of the sling line 60 toward the right which, in turn, raises the mast structure 13. The mast structure 13 is first raised off the ground a sufficient distance to allow the pinning on of the racking board assembly 50. Thereafter, the mast structure 13 is raised to its vertical position as indicated by the solid line construction in FIG. 5. The mast structure 13 is then pinned to the gin pole structure 21 by means of the coupling brackets 42. Thereafter, the sling line 60 is untied and removed from the mast structure 13.

Next, the walkway support extension 28 is swung up to its horizontal position and braced by brace 29, as shown in FIG. 6. Then, the skid 56 carrying the rotary table 55 and the rotary drive and catworks mechanism 57 is raised by means of the traveling block 'and moved onto the gin pole pedestal structure 18. At this time, the skid 56 is moved a sufficient distance to the left to that it is completely supported by the pedestal structure 18. Thereafter, the pipe setback pedestal structure 30 is moved into the horizontal position indicated in solid line in FIG. 6. The right-hand legs of the pedestal structure 30 are then pinned to the right-hand shoes 32 on the base structure 14. Thereafter, a tie line 61 is connected between the setback pedestal structure 30 and the hook of the traveling block 45. Traveling block 45 is then raised to move the setback pedestal structure 30 to its upright position as indicated by the dash line construction in FIG. 6. Tie line 61 is then removed and the left-hand legs of the pedestal strucutre 30 are pinned to the left-hand shoes 32 on the base structure 14. The skid 56 is then moved to the right until it contacts the setback pedestal 30, following which the right-hand end of the skid 56 is pinned to the pedestal structure 30 by way of appropriate pins and coupling brackets. The deck panels forming the working floor 11 are then set in place, as are the various handrails, stairs, ramps and other auxiliary structures normally associated with a drilling rig. The drilling rig is then in a condition to commence the drilling of a borehole into the earth.

Referring now to FIG. 7, there is shown a modified form of construction for both the rotary table support structure and the gin pole structure. The parts which remain the same as inthe FIG. 1 embodiment are identified by the same reference numerals as in FIG. 1. As seen in FIG. 7, the two self-supporting pedestal structures l8 and 30 are pinned to the base structure 14 on opposite sides of the mast structure 13 in the same manner as in the FIG. 1 embodiment. In the FIG. 7 embodiment, however, the rotary table support structure is comprised of a horizontally extending frame structure 62 which is pinned at one end to the first pedestal structure 18 and at the other end to the second pedestal structure 30. This frame structure 62 includes front and rear beams,only the first of which is visible in FIG. 7, which extend between the pedestal structures 18 and 30, together with appropriate crossbeams running therebetween. The rotary table is carried by the frame structure 62. Such frame structure 62 extends through the framework of the mast structure 13 and is not in direct contact therewith so that the rotary table 55 is supported independently of such mast structure 13. The rotary drive and catworks mechanism 57 in this embodiment is supported atop the pedestal structure 18, there being no skid used in this embodiment.

In place of the gin pole structure of the earlier embodiment, the sheaves used in raising the mast structure 13 are, in the FIG. 7 embodiment, rotatably mounted directly on the pedestal structure 18. More particularly, a pair of front and rear sheaves 63, only the front one of which is visible in FIG. 7, are used to handle the sling line used in raising the mast structure 13. As such, they take the place of the sheaves 24 and 26 of the earlier embodiment. A further sheave 64 is rotatably mounted at the back end of the pedestal structure 18 and in a central position along the backside thereof. This sheave 64 is used for guiding the drilling line 47 when raising the mast structure 13. As such, the sheave 64 takes the place of the gin pole sheave 25 of the FIG. 1 embodiment.

Except for the foregoing differences, the remainder of the drilling rig of FIG. 7, including the parts not shown, may be of the same construction as described in connection with the FIG. 1 embodiment.

While there have been described what are at present considered to be preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, intended to cover all such changes and modifications as fall within the true spirit and scope of the invention. r

What is claimed is:

l. A high floor pivoted mast drilling rig comprising:

a base structure;

. an upright framework type mast structure pivotally mounted on the base structure;

a first self-supporting pedestal structure mounted on the base structure on one side of the mast structure pivot axis for supporting a working floor at an elevated position above the base structure;

a racking board assembly carried by the mast structure at an upper location thereon and extending outwardly from the mast structure on the side farthest removed from the first pedestal structure; second self-supporting pedestal structure mounted on the base structure on the other side of the mast structure pivot axis and below the racking board assembly for supporting the lower end of racked drill pipe independently of the mast structure and at an elevated position above the base structure; and

a rotary table support structure extending through the framework of the mast structure and supported by the first and second pedestal structures at an e'levated position above'the base structure for supporting a rotary table independently of the mast structure.

2. A drilling rig in accordance with claim 1 and including sheave means supported by the first pedestal structure for use in raising the mast structure to an upright position.

3. A drilling rig in accordance with claim 1 and including gin pole means carried by the first pedestal structure and base structure and extending upwardly therefrom and a plurality of sheaves rotatably carried by the upper portion of the gin pole means for use in raising the mast structure to an upright position.

4. A drilling rig in accordance with claim 1 and including a plurality of sheaves rotatably mounted on the first pedestal structure for use in raising the mast structure to an upright position. I

5. A drilling rig in accordance with claim 1 wherein the first and second pedestal structures are detachably connected to the base structure.

6. A drilling rig in accordance with claim 1 wherein the first and second pedestal structures are boxlike framework type structures having four legs pinned to the base structure.

'7. A drilling rig in accordance with claim 1 and including a rotary table mounted on the rotary table support structure and located so that the center of the rotary tabel is within the confines of the framework of the mast structure. I

.8. A drilling rig in accordance with claim 7 an including hoisting means carried by the mast structure, draworks located adjacent the first pedestal structure at an elevation considerably lower than the elevation of the rotary table support structure, an independent rotary drive mechanism carried by the first pedestal structure at about the same elevation as the rotary table and linkage means for operatively coupling the rotary drive mechanism to the rotary table. V I

9. A drilling rig in accordance with claim 1 wherein the rotary table support structure comprises a skid structure resting on an upper portion of the first pedestal structure and extending through the framework of the mast structure and connected to an upper portion of the second pedestal structure.

10. A drilling rig in accordance with claim 9 wherein the skid structure carries a rotary table the center of which is loacted within the confines of the framework of the mast structure, a rotary drive mechanism located to the first pedestal structure side thereof and linkage means operatively coupling the rotary drive mechanism to the rotary table.

11. A drilling rig in accordance with claim 1 wherein the rotary table support structure comprises a horizontally extending frame structure connected at one end to the first pedestal structure and connected at the otherv end to the second pedestal structure and the drilling rig includes a rotary table carried by this horizontally extending frame structure and located so that the center of the rotary table is within the confines of the frameowrk of the mast structure. 

1. A high floor pivoted mast drilling rig comprising: a base structure; an upright framework type mast structure pivotally mounted on the base structure; a first self-supporting pedestal structure mounted on the base structure on one side of the mast structure pivot axis for supporting a working floor at an elevated position above the base structure; a racking board assembly carried by the mast structure at an upper location thereon and extending outwardly from the mast structure on the side farthest removed from the first pedestal structure; a second self-supporting pedestal structure mounted on the base structure on the other side of the mast structure pivot axis and below the racking board assembly for supporting the lower end of racked drill pipe independently of the mast structure and at an elevated position above the base structure; and a rotary table support structure extending through the framework of the mast structure and supported by the first and second pedestal structures at an elevated position above the base structure for supporting a rotary table independently of the mast structure.
 2. A drilling rig in accordance with claim 1 and including sheave means supported by the first pedestal structure for use in raising the mast structure to an upright position.
 3. A drilling rig in accordance with claim 1 and including gin pole means carried by the first pedestal structure and base structure and extending upwardly therefrom and a plurality of sheaves rotatably carried by the upper portion of the gin pole means for use in raising the mast structure to an upright position.
 4. A drilling rig in accordance with claim 1 and including a plurality of sheaves rotatably mounted on the first pedestal structure for use in raising the mast structure to an upright position.
 5. A drilling rig in accordance with claim 1 wherein the first and second pedestal structures are detachably connected to the base structure.
 6. A drilling rig in accordance with claim 1 wherein the first and second pedestal structures are boxlike framework type structures having four legs pinned to the base structure.
 7. A drilling rig in accordance with claim 1 and including a rotary table mounted on the rotary table support structure and located so that the center of the rotary tabel is within the confines of the framework of the mast structure.
 8. A drilling rig in accordance with claim 7 an including hoisting means carried by the mast structure, draworks located adjacent the first pedestal structure at an elevation considerably lower than the elevation of the rotary table support structure, an independent rotary drive mechanism carried by the first pedestal structure at about the same elevation as the rotary table and linkage means for operatively coupling the rotary drive mechanism to the rotary table.
 9. A drilling rig in accordance with claim 1 wherein the rotary table support structure comprises a skid structure resting on an upper portion of the first pedestal structure and extending through the framework of the mast structure and connected to an upper portion of the second pedestal structure.
 10. A drilling rig in accordance with claim 9 wherein the skid structure carries a rotary table the center of which is loacted within the confines of the framework of the mast structure, a rotary drive mechanism located to the first pedestal structure side thereof and linkage means operatively coupling the rotary drive mechanism to the rotary table.
 11. A drilling rig in accordance with claim 1 wherein the rotary table support structure comprises a horizontally extending frame structure connecteD at one end to the first pedestal structure and connected at the other end to the second pedestal structure and the drilling rig includes a rotary table carried by this horizontally extending frame structure and located so that the center of the rotary table is within the confines of the frameowrk of the mast structure. 